1. Field of the Invention
The invention relates to a method of working a device and a method of working a slider. More particularly, the invention relates to a method of working a device and a method of working a slider for cutting and individually separating devices or sliders which are formed on one substrate and require smoothness of the side and front surfaces thereof.
2. Description of the Related Art
A slider for a magnetic head for use in a magnetic recording apparatus such as a hard disc driver (hereinafter referred to as HDD) is manufactured through steps generally shown in FIGS. 8A to 8F, for example.
First, a plurality of devices 1 such as a transducer having a function of writing/reading information as the magnetic head are formed on a substrate 2 such as a ceramic substrate (see FIG. 8A).
Then, the substrate 2 is cut so as to be rectangular (see FIG. 8B). Then, the rectangular substrate 2 is further sliced into bars, each of which has a line of about ten or more devices 1 horizontally arranged, and bars 3 are separated from one another (see FIG. 8C). Heretofore, such cutting has been generally performed by using a diamond peripheral cutting edge. Then, each of the separate bars 3 is stuck on a suspension 4 with wax (not shown) or the like (see FIG. 8D). Sticking is temporary bonding such that the sliders can be separated from the suspension 4 after the sliders are completely individually separated from one another in the following step.
Then, each of the devices 1 arranged on the bar 3 is worked as the slider. That is, a head slider surface is ground, structures such as a groove for determining a width of a slider rail and a bleed slot surface are worked, and a head levitation surface, i.e., a slider rail surface is polished so as to have predetermined surface roughness of 0.05 xcexcm or less, for example. Furthermore, an air inlet for functioning as an air bearing surface of the slider rail surface is tapered (see FIG. 8E).
After the structure of a principal part of the slider is thus formed, sliders 6, each of which comprises each of the devices 1 worked in a unit of the bar 3, are separated one by one by cutting the bar 3 at a boundary between adjacent sliders 6 (see FIG. 8F).
Then, chamfering (so-called blending) takes place (not shown). In order to prevent the slider from doing damage to the surface of a magnetic recording medium (a magnetic disk) at the time of contact start/stop when the slider mounted as a slider head is used in the HDD, chamfering is applied to more particularly an edge of the slider rail surface which is likeliest to contact the surface, additionally an edge line portion which is likely to contact the surface of the magnetic recording medium (the magnetic disk) and so on. Heretofore, the slider for the magnetic head for use in the magnetic recording apparatus such as the HDD has been manufactured through such a manufacturing process.
In the above-described step of working the slider for the magnetic head of the related art, more particularly, in the step of individually separating the sliders by cutting the bar 3, cutting is generally done by using a diamond sharp edge grinding wheel (a diamond peripheral cutting edge saw).
However, such a cutting method of the related art using the diamond sharp edge grinding wheel has the following various problems. That is, the cutting method itself using the diamond sharp edge grinding wheel essentially has mechanical characteristics of cutting the bar 3 while applying a large shearing force to the bar 3, and thus a surface cut by the diamond sharp edge grinding wheel results in a crushed surface or a streaked surface. The surface roughness of the cut surface that is the crushed surface or the streaked surface can only be smoothed to about 20 nm in terms of Ra even through an approach of reducing roughness of the diamond sharp edge grinding wheel and others. So-called contamination such as external dust or particles or dust produced within the HDD itself is prone to adhere to such a rough surface.
Therefore, a problem exists. During the use of the HDD, such contamination peels off due to vibration generated during operation of the slider head, vibration created during carrying of the HDD itself or the like, and the contamination adheres to the surface of the magnetic disk that is the recording medium, or the contamination is attracted into a gap between the magnetic disk and the slider. Consequently, the contamination damages the surface of the magnetic disk.
There exists another problem. Adhesion of contamination to the surface of the magnetic disk causes a record or read malfunction such as a read/write error resulting from thermal asperity. Moreover, in the cutting method using the diamond sharp edge grinding wheel, the cut surface has the crushed surface or the streaked surface as described above. In other words, the fact that the cut surface has the crushed surface or the streaked surface means that cutting takes place while such a large shearing force is applied to the bar 3. Accordingly, high stress is applied to the bar 3 due to such a large shearing force applied during cutting. As a result, the overall shape of the cut bar 3 remains under stress strain.
Thus, the individual sliders obtained through cutting have a problem: various failures deteriorating profile precision for the slider occur. Failures include malformation, namely, convex or concave warping called a crown; poor inclination along the width of the slider rail of the air bearing surface, called a camber; poor parallelism along a length of two slider rails of the air bearing surface, called a twist (i.e., the relative positions of two slider rails are in a state in which two slider rails are not parallel to each other but twisted); and so on.
More particularly, in recent years, a further increase in an information recording density has been strongly demanded. The increase in the information recording density requires a further reduction in magnetic spacing. The reduction in the magnetic spacing is accomplished by more precisely controlling and thus further reducing a height of levitation of the slider from the recording medium. An approach of reducing a conventional height of levitation of about 40 nm to 50 nm by more than half, i.e., to about 10 nm to 20 nm and others have been also proposed. In order to realize the purpose, it is therefore strongly demanded that the air bearing surface (hereinafter referred to as ABS) is more highly precise, roughness-free, smooth and flat.
However, the cutting method of the related art using the diamond sharp edge grinding wheel has a problem of being unable to cope with a further improvement in precision of the ABS for a recent increase in the information recording density because various failures deteriorating the profile precision for the slider occur as described above.
Moreover, due to a large shearing force applied to the bar 3 during cutting as described above, protrusions of about 2 nm to 10 nm or asperities are produced at an edge at which the cut surface crosses the surface of the ABS. There is a problem that the protrusions or asperities also cause deterioration in the profile precision for the slider similarly to the above-mentioned various malformations. Although the precision of the ABS generally needs a cross crown of 10 nm or less in order to improve stability of levitation of the slider and increase the information recording density, the cutting method of the related art using the diamond sharp edge grinding wheel has a problem of being unable to cope with the need.
Moreover, the following problem exists. Chippings of about 1 nm to 20 nm are produced at the edge at which the surface of the ABS crosses the cut surface obtained by the diamond sharp edge grinding wheel and the edge at which a rear surface opposite to the ABS crosses the cut surface obtained by the diamond sharp edge grinding wheel. Similarly to the above-mentioned contamination such as dust, the chippings peel off the slider due to vibration, shock or the like during the use of the HDD, and thus the chippings damage the surface of the magnetic disk as the contamination or cause the malfunction such as the read/write error resulting from the thermal asperity.
The HDD of the related art is manufactured in a clean room whose cleanness is comparable to that of class 100 or more for a process of manufacturing LSI in order to prevent contamination from entering the HDD at the time of manufacturing. Moreover, an air filter is included in the HDD so as to cope with mainly external contamination. Such an approach allows coping with an entry of contamination during manufacturing and an entry of external contamination.
However, during manufacturing, the contamination produced by peeling of chippings as described above adheres to the cut surface still in the form of chipping. The chippings are not recognized as a cause of failures. Thus, the chippings are likely to cause malfunction at the time of an actual use of the HDD, but the chippings are not checked and are overlooked. At the time of the actual use of the HDD, the slider having the adhering chippings makes a relative movement over the nearly overall surface of the magnetic disk. Thus, the slider is always located on or near the magnetic disk whenever the chippings peel off. Thus, almost all the particles of the peeling chippings always drop onto and adhere to the magnetic disk. Consequently, there is a problem that the particles produced by the peeling of the chippings are extremely likely to damage the surface of the magnetic disk or cause the read/write error as the contamination.
In any of the above-mentioned cases, the slider including a magnetic head function portion such as the transducer has been described as the device 1 to be separated of the typical related art. However, it is needless to say that the type of device is not limited to only this type. An example of the type of devices to be individually separated after being formed is a contact-type image sensor comprising, for instance, a staggered arrangement of a plurality of optical sensor devices. Nearly the same problems of the cut surface as the above-mentioned problems arise in a step of separating a plurality of optical sensor devices, or the like. Moreover, nearly the same problems of the cut surface as the above-mentioned problems arise in a step of separating levitation-type heads of a structure in which an optical module for magneto-optical recording, instead of the magnetic head, is mounted on a tip of a suspension arm, or the like. Furthermore, nearly the same problems of the cut surface as the above-mentioned problems arise in a step of separating levitation-type heads of a structure having both of a magnetic head and an optical head for magneto-optical recording, or the like. Furthermore, nearly the same problems of the cut surface as the above-mentioned problems arise in a step of separating contact-type magnetic heads or optical heads including a contact pad for contacting the surface of the magnetic disk without damaging the surface of the magnetic disk, or the like.
In order to eliminate the roughness of the cut surface and the chippings described above, the final cut surfaces of each of the individual devices or sliders must be polished or subjected to other processes after the devices or sliders are completely cut and individually separated. A technique of individually polishing the sliders through such a step is proposed in Japanese Patent Laid-open No. Hei 6-282831, for example. However, a step of lapping each of the cut surfaces of each slider after individually separating the devices or sliders is extremely complicated, and thus the time required for the step is long. That is, in a conventional method in which polishing such as lapping is applied to the sliders individually separated, a step of attaching each of the individually-separated sliders to a lapping apparatus and lapping four side surfaces of each slider, i.e., the cut surfaces of each slider is an extremely complicated step. Thus, the conventional method has a problem that a throughput of the step is inefficient and thus the step requires a long time.
The invention is designed to overcome the foregoing problems. It is an object of the invention to provide a method of working a device and a method of working a slider, which solve the problem of the deterioration in the profile precision and the problem of the contamination resulting from the roughness of the cut surface or the chippings in a cutting step of individually separating a plurality of devices formed on one substrate, thereby being capable of manufacturing the slider for implementing the magnetic head that is available for the HDD with high reliability without causing the damage to the magnetic disk and the read/write error when the magnetic head, for example, is incorporated and used in the HDD.
A method of working a device of the invention for individually separating a plurality of devices formed on one substrate comprises: a supporting step for allowing a suspension to support the devices on a rear surface opposite to a front surface of the substrate on which the devices are formed; a notching step for cutting a notch at a boundary set between the devices on the substrate to some midpoint of a thickness of the substrate along the thickness of the substrate from the front surface of the substrate; and a substrate cutting step for bringing a wire saw of a diameter greater than a width of the notch into contact with the notch, and slicing the substrate across the overall thickness of the substrate along the thickness of the substrate while sliding the wire saw in a longitudinal direction, thereby smoothing a cut surface formed by cutting while cutting the substrate.
Another method of working a device of the invention for individually separating a plurality of devices formed on one substrate comprises: a supporting step for allowing a suspension to support the devices on a rear surface opposite to a front surface of the substrate on which the devices are formed; a first cutting step for cutting a boundary set between the devices on the substrate across the overall thickness of the substrate along the thickness of the substrate from the front surface of the substrate; and a second cutting step for bringing a wire saw of a diameter greater than a width of a portion cut by the first cutting step into contact with the portion, and slicing the substrate across the overall thickness of the substrate along the thickness of the substrate while sliding the wire saw in a longitudinal direction, thereby smoothing a cut surface formed by cutting while cutting the substrate.
A method of working a slider of the invention for individually separating a plurality of sliders formed on one substrate comprises: a supporting step for allowing a suspension to support the sliders on a rear surface opposite to a front surface of the substrate on which the sliders are formed; a notching step for cutting a notch at a boundary set between the sliders on the substrate to some midpoint of a thickness of the substrate along the thickness of the substrate from the front surface of the substrate; and a substrate cutting step for bringing a wire saw of a diameter greater than a width of the notch into contact with the notch, and slicing the substrate across the overall thickness of the substrate along the thickness of the substrate while sliding the wire saw in a longitudinal direction, thereby smoothing a cut surface formed by cutting while cutting the substrate.
Another method of working a slider of the invention for individually separating a plurality of sliders formed on one substrate comprises: a supporting step for allowing a suspension to support the sliders on a rear surface opposite to a front surface of the substrate on which the sliders are formed; a first cutting step for cutting a boundary set between the sliders on the substrate across the overall thickness of the substrate along the thickness of the substrate from the front surface of the substrate; and a second cutting step for bringing a wire saw of a diameter greater than a width of a portion cut by the first cutting step into contact with the portion, and slicing the substrate across the overall thickness of the substrate along the thickness of the substrate while sliding the wire saw in a longitudinal direction, thereby smoothing a cut surface formed by cutting while cutting the substrate.
In the method of working a device or the method of working a slider of the invention, the notch is previously cut to some midpoint of the thickness of the substrate, or the wire saw is brought into contact with the notch previously cut by the first cutting step. In this case, the notch previously formed serves as a guideline and guides the wire saw to an appropriate boundary, i.e., a cutting position by self alignment, whereby cutting takes place at a precise position. Moreover, the wire saw passes through a portion which is already cut with a small width or is cut to at least some midpoint of the thickness. Thus, only a very small shearing force is applied to the substrate from the viewpoint of the strength of materials, compared to the shearing force for a method of the related art in which one cutting takes place using a diamond grinding wheel. Only a small shearing force such as is substantially close to the shearing force for polishing rather than the shearing force for general cutting is applied to the substrate.
Therefore, the substrate can be cut with high precision while the cut surface is smoothed at the time of cutting using the wire saw, without causing deterioration in profile precision, roughness of the cut surface, chipping or the like as in the related art. Moreover, the method of the invention can cut the substrate with high precision for a short time and can also make smoothness of the cut surface excellent, compared to a technique proposed in, for example, Japanese Patent Laid-open No. Hei 4-195706, No. Hei 7-296377 or the like in which the substrate is cut by only one cutting step using the wire saw so as to individually separate magnetic heads.
One reason is as follows. In the case of a cutting method according to the invention, the notch is previously provided as described above and thus the notch allows the wire saw to be guided to the precise position by self alignment. Another reason is that the wire saw can always do cutting with the precise diameter portion thereof by appropriately shifting the worn portion thereof and thus an error of a cutting allowance can be reduced. Moreover, the wire saw cuts a portion which is previously cut although a width of cut is small as described above, and thus final cutting can be done by a small shearing force alone. Accordingly, a speed at which the wire saw slices the substrate along the thickness of the substrate at the time of cutting can be made faster than a cutting speed of the wire saw of the related art (e.g., Japanese Patent Laid-open No. Hei 4-195706). In other words, the slicing time can be made shorter than the cutting time of the related art. Moreover, the cut surface obtained through cutting can have excellent smoothness.
In the method of working a device or the method of working a slider of the invention, the notching step for cutting the notch or the first cutting step for performing first cutting may be performed by the use of the diamond grinding wheel. Alternatively, these steps may be also performed by the use of the wire saw whose diameter is smaller than that of the wire saw for the second cutting step.
The suspension for supporting the devices or the sliders on the rear surface thereof may be joined to the rear surface of the substrate in such a manner that the overall surface of the suspension is in contact with the rear surface of the substrate. Alternatively, the suspension may be joined to only the devices or the sliders so as not to be joined to the cutting allowance between the devices or the sliders, thereby supporting the devices or the sliders by only the joint portions.
Moreover, in the method of working a slider of the invention, it is desirable that the substrate cutting step uses both of slurry containing abrasive grains having a particle diameter of 5 xcexcm or less and the wire saw.
That is, an empirical rule that a damaged layer and a chipping produced at the time of cutting are both 5 xcexcm at the maximum has been heretofore obtained from previous practical manufacturing experience. It is therefore desirable that the substrate is cut by the wire saw by using the slurry containing abrasive grains having a particle diameter of 5 xcexcm or less in order to control a stock allowance equal to or less than 5 xcexcm, i.e., a size of the damaged layer and the chipping. More preferably, the particle diameter of the abrasive grain for use in the slurry is equal to about 1 xcexcm. If the size is less than 1 xcexcm, cutting efficiency, in fact, tends to decrease. If the abrasive grain has a particle diameter exceeding 5 xcexcm, the abrasive grain does not differ much from a conventional diamond grinding wheel and thus there is a tendency to be incapable of obtaining smoothness and precision required for the slider. Accordingly, in consideration of such a qualitative tendency, the particle diameter of the abrasive grain for use in the slurry can be appropriately determined within a range of a particle diameter of 5 xcexcm or less so that the particle diameter can be adapted to the required smoothness and precision in dimension of cut.
If an amount of removal by the wire saw is too large, cutting does not differ much from cutting using the conventional diamond grinding wheel and thus a problem arises: the shearing force increases and the cutting time also increases. It is therefore desirable that a difference in dimension between the width of cut (gap) by the first cutting step and the diameter of the wire saw is equal to 5 xcexcm to 15 xcexcm per cut surface. However, the difference in dimension is not limited to these values. For example, when the width of the damaged layer produced by the first cutting step or the size of the chipping is larger than 5 xcexcm, it is, of course, desirable that the wire saw having such a diameter as can ensure the removal of the damaged layer or the chipping is used.
Powders of diamond, sapphire or the like for a general abrasive grain can be used as a material of the above-mentioned abrasive grain. When the slurry is not used, the wire saw having abrasive grains deposited to a wire itself, such as a diamond-electrodeposited wire saw, can be used.
Moreover, the devices or the sliders may be removed from the suspension after the cutting step according to the invention. Alternatively, for example, the suspension is made of an insulating material and the substrate is cut together with the suspension into the individual devices or sliders, whereby the insulating suspension can be used as an insulating layer in each device or slider finally obtained. In short, the suspension may be also used as a part of a structure of each of the devices or sliders such as the insulating layer, without being removed from the individual devices or sliders.
Other and further objects, features and advantages of the invention will appear more fully from the following description.